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Bunker Fuel Quality

Gard: Cashew Nut Shell Liquid blends – a marker for a problematic fuel?

Gard has handled claims where the presence of phenolic compounds originating from CNSL in conventional fuels has resulted in operational problems or machinery damage for vessels.

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RESIZED Shaah Shahidh on Unsplash

Maritime protection and indemnity (P&I) club Gard recently published an insight on Cashew Nut Shell Liquid (CNSL) and several cases it has handled involving the detection of phenolic compounds originating from CNSL in conventional fuels, which has resulted in operational problems or machinery damage for vessels.

Capt. Rahul Choudhuri of VPS assisted with this article:

Growing demand for low to zero carbon fuels across transport sectors to meet environmental regulations has increased interest in alternative sources. Fatty Acid Methyl Esters (FAME) are popular for biofuels, but high demand across various transport sectors exceeds supply. Cashew Nut Shell Liquid (CNSL), a byproduct of the cashew industry, is considered an alternative source of biofuels. 

What is CNSL?

Cashew Nut Shell Liquid, a cost-effective renewable fuel, differs from FAME biofuels. As a substituted phenol, its high reactivity and lower stability are attributed to its elevated iodine value. Beyond its fuel potential, CNSL is already used in the production of plastics, resins, adhesives, laminates, and surface coatings. Its high acid value (> 3mgKOH/g) also makes it significantly corrosive. CNSL’s key phenolic compounds that tend to polymerize, forming gums and fuel deposits include: 

  • Anacardic Acid is a major contributor to CNSL’s high acidity. Thermal decarboxylation converts this to cardanol, reducing acidity and enhancing stability.
  • Cardanol, also known as Ginkgol, is a stable phenolic compound derived from anacardic acid with improved combustion and lubricity properties.
  • Cardol, also referred to as Olivetol, is a dihydroxybenzene derivative with surfactant-like behaviour.

Cases of CNSL causing operational problems

Cashew Nut Shell Liquid, despite its benefits of increased lubricity and energy content, poses challenges due to high acidity, poor combustion, and corrosiveness. Widespread contamination of conventional fuels with CNSL was reported in the ARA region in 2022, leading to operational problems such as fuel sludging, fuel injector failure, engine part corrosion, filter clogging, fuel system deposits, turbocharger nozzle ring corrosion, fuel pump plunger and barrel wear, and damage to Selective Catalytic Reactor (SCR) units. Since these incidents, Gard has handled several cases involving the detection of phenolic compounds originating from CNSL in varying concentrations.

Case study 1

A vessel bunkered HSFO in Southeast Asia. Despite passing initial ISO 8217, Table 2 testing and preliminary GCMS screening, the fuel soon caused main engine exhaust temperature alarms, followed by leaking injectors and stuck fuel valves. The vessel required an 800nm tow to safety. Subsequent GCMS revealed over 10,000 ppm of Cardonol. Costs incurred exceeded USD 800,000.

Case study 2

A vessel experienced significant operational issues shortly after using ULSFO that initially passed ISO 8217, Table 2 testing. Fuel was stemmed at a port in Northern Europe. Problems included high main engine exhaust temperatures, auxiliary engine failure and fuel leaks, fouled nozzles, and damaged high-pressure fuel pipes, necessitating replacement of all fuel pumps and valves. GCMS analysis revealed high levels of Cardanol (> 30,000 ppm), Cardol (> 5,000 ppm), and Anacardic Acid (> 1,000 ppm) totalling 1.24% by mass of the fuel composition. The cost of repairs exceeded USD 400,000.

We are aware of several vessels having been impacted by the same bunker delivery.

cashew nut shell mchinery

It is worth noting that there have been instances where CNSL-blended conventional fuels have been stored and combusted without any operational issues being reported.

Testing of CNSL as biofuel – VPS’s experience

VPS, in their recently published article ‘Cashew Nut Shell Liquid – Biofuel Saviour or Concerning Contaminant?’ shared the results of their testing of CNSL products, blended with marine gas oil (MGO), very low sulphur fuel oils (VLSFO) and high sulphur fuel oils (HSFO). Fuel Combustion Analysis (FCA) revealed a spectrum of outcomes for estimated cetane number, ignition delay, and rate of heat release (ROHR), with CNSL blends showing a performance gradient: the HSFO blend performed particularly poorly, the VLSFO blend showed improvement, and the MGO blend yielded the most favourable results.

Whether the blends were 80/20, 70/30 or 50/50 Fossil/CNSL, the blends using HSFO consistently gave the poorest FCA results. This may be due to a negative interaction between the asphaltenic content of the HSFO and the acidic nature of the CNSL. Each of the CNSL blends gave poorer FCA results when compared with the 100% fossil fuels, HSFO, VLSFO, MGO and 100% FAME.

They have also shared a B100 case study, where the fuel was assumed to be 100% FAME, but the analysis revealed that it was 40% FAME, 10% FAME Bottoms and 50% CNSL. Technically, the fuel was still B100, but with the Biomass comprising of different components. This emphasizes the importance of due diligence regarding fuel procurement for charterers and owners.

CNSL and ISO 8217

One of the experts Gard consulted reported that “CNSL is not a permissible component in bunker fuels, on the basis that same is not a hydrocarbon derived from petroleum refining, nor is it derived from an alternative permissible hydrocarbon source and thus falls foul of Clause 5 of ISO 8217.” VPS comments along the same lines in their alert “For the purposes of ISO 8217:2024 and all preceding versions, CNSL is not recognized as a standard fuel component. Accordingly, its presence in a marine fuel may be considered a contaminant and potentially classified as off-specification when assessed against the ISO 8217 standard”.

It’s important to note that Annex B of ISO 8217:2024 acknowledges that various chemical species or materials (though not exhaustively listed) can cause operational issues. Consequently, fuel oil purchasers might need to conduct advanced testing to identify substances that could render the fuel unsuitable for the engines. Moreover, although ISO 8217:2024 addresses biofuels, its scope does not extend to all forms of biomass

Note: The full article by Gard including key recommendations can be found here

Related: VPS on Cashew Nut Shell Liquid: Biofuel saviour or concerning contaminant?

 

Photo credit: Shaah Shahidh on Unsplash and Gard
Published: 29 May, 2025

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Research

Integr8 Fuels report shares comprehensive analysis of Mediterranean ECA

Data reveals a market in rapid transition, confirming some industry predictions while uncovering new, emerging risks for ship operators.

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Integr8 Fuels trading intelligence (July 2025)

International bunker trading firm Integr8 Fuels on Monday (7 July) shared its new report ‘Mediterranean ECA: Immediate Operational and Commercial Impact of Implementation’ which provides the first comprehensive analysis of the rule’s effects on fuel quality and regional availability.

The data reveals a market in rapid transition, confirming some industry predictions while uncovering new, emerging risks for ship operators. The following key findings include:

  1. Dramatic Supply Shift Confirmed: VLSFO Availability Contracts Sharply. VLSFO’s share of the Mediterranean fuel market has plummeted from over 60% in December to just 37.5% in May. In parallel, the number of ports supplying VLSFO has fallen by 47%, creating new logistical challenges for vessels that continue to use the grade.
  2. VLSFO Instability Spikes as Supply Chain Adapts. Very Low Sulphur Fuel Oil (VLSFO) off specification rates more than doubled from 1.5% in December to 3.8% in May. Critically, one in four (25%) of these off-specs were for total sediment potential (TSP), indicating a rising risk of sludge formation that can damage engines. This trend appears linked to extended in-tank storage and the consolidation of older fuel stocks as demand slows and suppliers pivot away from VLSFO.
  3. Persistent Flash Point Risks in Key LSMGO Hubs. Flash point non-conformance has increased significantly and now accounts for over two-thirds of all LSMGO off specs. Our data shows this is not a random problem, with over 75% of all flash point incidents concentrated in Spain, Turkey, and Italy, signalling a persistent potential for SOLAS violations in core supply zones.

Note: The full report may be obtained from Integr8 Fuels here.

 

Photo credit: Integr8 Fuels
Published: 8 July 2025

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Contamination

VPS advises on effects of FAME contamination in bio bunker fuels on engine oils

Stanley George highlights that engines operating on FAME-based bio bunker fuels are more susceptible to rapid oil viscosity degradation, where FAME does not evaporate easily, leading to cumulative effects.

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Stanley George, Group Science & Technical Manager of marine fuels testing company VPS, on Monday (23 June) highlighted engines operating on FAME-based biofuels are more susceptible to rapid oil viscosity degradation, where FAME does not evaporate easily, leading to cumulative effects:

Engines running on Bio-blends containing Fatty Acid Methyl Esters (FAME), especially pure FAME, e.g. 100% FAME can experience decreased engine oil viscosity over time.

Fuel oil contamination in engine lubricants is a known phenomenon, and most marine-grade engine oils are formulated to tolerate certain levels of such contamination while maintaining operational performance.

The impact of FAME contamination is more pronounced in four-stroke trunk piston engines due to their design and operational characteristics. These engines use a common oil sump for both crankcase and cylinder lubrication, making them more vulnerable to fuel ingress through injector leaks or blow-by gases. Unlike two-stroke crosshead engines, which have separate lubrication systems that limit fuel-oil interaction, four-stroke engines continuously recirculate the same oil, allowing FAME (which has a high boiling point and low volatility), to accumulate over time. This leads to a more significant reduction in oil viscosity and faster degradation of lubricating properties.

A typical SAE (Society of Automotive Engineers) 30 grade engine oil has a viscosity of about 90 to 110 cSt at 40°C and a B100 (100% FAME) or its fossil counterpart such as DMA (distillate fuel) has a viscosity in the range of 4 cSt at 40°C. Any contamination of the fuel (distillate or Bio distillate blends contain FAME) into the used engine oil can therefore significantly reduce the viscosity of the used engine oil.

Most OEMs specify both minimum and maximum viscosity limits for engine oils, beyond which the engine must not be operated to avoid wear or lubrication failure. For example, a common condemning limit is a 25% reduction in viscosity at 40°C from the fresh oil value. In the case of an SAE 30 grade oil (with a typical fresh viscosity of around 90 cSt at 40°C), this corresponds to a minimum allowable limit of approximately 67 cSt.

When comparing the viscosities of distillate fuel and B100, there is no significant difference (both typically range between 3 to 5 cSt at 40°C). However, a noticeable drop in engine oil viscosity is not usually observed when engines operate on conventional distillate fuel. This is likely due to the higher volatility and lighter fractions present in fossil fuels, which tend to evaporate over time. Additionally, the routine top-up of fresh oil during engine operation, needed to compensate for losses from evaporation and leakage, helps maintain a more stable overall oil viscosity. As a result, the dilution effect is minimised, and the lubricating oil retains its properties for a longer duration compared to operation on B100.

Distillation Behaviour Analysis of FAME

ISO 3405 is an international standard that outlines a laboratory method for determining the distillation characteristics of petroleum and related products at atmospheric pressure. This tests helps us to understand the composition and behaviour of fuel during storage and use including the tendency to form vapours.

Typically in this method, the sample is distilled under controlled conditions. Throughout the distillation, the temperature at which specific volumes of the sample evaporate is recorded. Key measurements include, Initial Boiling Point (IBP) -Temperature at which the first drop of condensate is collected, Final Boiling Point (FBP) -Temperature at which the last drop of liquid evaporates and temperature at Specific Recovery Percentages, temperatures corresponding to 10%, 50%, and 90% volume recovery, among others. The collected data is used to construct a distillation curve, which illustrates the boiling behaviour of the sample.

In order to understand this phenomenon we compared the distillation characteristic of a 100% FAME (B100), 30% FAME (B30) and pure straight run distillate fuel using the ISO 3405 method. Below is a graph illustrating the differences in the distillation characteristics.

VPS advises on effects of FAME contamination in bio bunker fuels on engine oils

Note: The full article by VPS can be viewed here

 

Photo credit: VPS
Published: 24 June, 2025

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Methanol

Auramarine launches water in methanol measurement technology

Water Content Analyser technology measures and reports concentration of water in methanol when used as a marine fuel, helping ship operators take action to minimise associated risks and costs.

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Auramarine launches water in methanol measurement technology

Finland-based fuel supply systems provider Auramarine on Tuesday (3 June) announced the launch of its Auramarine Water Content Analyser (AM Water Content Analyser). 

The technology measures and reports the concentration of water in methanol, helping ship operators take preventive action to minimise associated risks and costs when using the fuel. 

The analyser comes in response to growing uptake of methanol as a marine fuel to meet shipping’s decarbonisation targets. Water as a natural contaminant of methanol may be present in the bunkered methanol either by accident or intentionally. Water in fuel decreases the calorific heating value which increases the bunkering costs. In addition, if the water content is too high, operators may have to unload the fuel, leading to delays and additional costs.  

As an example, when a Ro-Ro vessel consumes 27 000 metric tonnes (mt) of green methanol in one year and with an average price per ton of green methanol at EUR 1,196 (USD 1,361), the operator of the vessel may avoid losses of up to EUR 1,614,600 for 5% concentration of water as contaminant. 

The AM Water Content Analyser is an inline measurement device that can be installed directly to the methanol process piping, for example to the main bunker line with the flanged housing. The technology uses a sensor to analyse the concentration of water in the methanol.

John Bergman, CEO of Auramarine, said: “Methanol uptake is increasing across the industry due to its promising Greenhouse Gas (GHG) emissions reduction credentials. At Auramarine, we’ve led the way in developing solutions that support the use of alternative fuels-starting with the industry’s first Methanol Fuel Supply Units in 2022. 

“Now, with the launch of our AM Water Content Analyser, we’re giving ship owners and operators the tools they need to take the next step in their energy transition and bunker methanol with greater confidence, and importantly, at a lower cost.”

 

Photo credit: Auramarine
Published: 4 June, 2025

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